19.M F Xu, H Zhang, S Zhang, L S Liao, W. Choy,et al. Journal of Materials Chemistry A (Accepted)

 A low temperature gradual annealing scheme for achieving high performance perovskite solar cells with no hysteresis

CH3NH3PbI3 is commonly used in perovskite solar cells due to its long diffusion length and good crystallinity. In this paper, in the onestep approach using CH3NH3I and PbCl2 for forming the perovskite, we present a new low temperature annealing approach of gradually increasing the temperature to fabricate perovskite films. Various temperatures and temperature ranges for the formation of perovskite films have been studied. Using the gradual annealing process, we can tune the amount of chlorine in the atomic ratio of chlorine/iodine from 1.2 to 4.0%. Meanwhile, the gradual annealing process influences the quality of perovskite film and importantly the device performance. The results show that through the optimized process, the film quality is improved with high surface coverage and good photoluminescence and reproducibility. We find that relatively higher amount of chlorine in the perovskite film plays a positive role on the device performance in the approach for achieving the power conversion efficiency of 14.9% with no obvious hysteresis.